This invention relates to an improved flotation mechanism for the mining industry and in particular for the process of separating minerals from ore through flotation of the mineral and removal from the ore.
In the mining/milling industry flotation remains the primary method for concentrating and recovering minerals such as copper, nickel, iron, molybdenum, lead and zinc sulfides, coal, phosphate and other minerals utilizing copper flotation, fine coal flotation, base metal sulfide flotation and precious metal sulfide flotation.
Flotation is essentially a three phase unit process involving the intimate mixing of finely ground solids, liquid, and air to concentrate desired minerals from gangue by floating one away from the other. In carrying out the flotation process, the ore is crushed into finely ground solids and mixed with liquid to form a slurry or pulp. The slurry is then aerated using a flotation machine to achieve solid/liquid mixing and air dispersion through an external air source or by a self-aspirating flotation machine. U.S. Pat. No. 4,425,232 describes a flotation separation apparatus and method comprising a flotation machine provided with a rotor-stator pump assembly submerged in a slurry and in which rotor blades agitate the slurry thoroughly mixing the solids and liquid and introducing air to the mixture for aeration and generation of froth or foam on the surface of the flotation cell. Particles of minerals attach to carrier air bubbles which are naturally buoyant and form the froth, this being the effective mechanism for mineral recovery. Ordinarily, a wetting agent is utilized to promote wetting of the mineral particles making them hydrophobic and promoting their attachment to air bubbles forming the froth. The froth is removed hydrodynamically from the top of the slurry mass together with the entrapped mineral particles which are recovered as the froth is accumulated and dried.
As disclosed in U.S. Pat. No. 4,425,232 the flotation mechanism comprises a pump having a rotor and a stator, and is hydrodynamically designed to issue radially discharging aerated jets of pulp from the mechanism. The rotor provides a strong pumping action to suspend slurry solids and disperses air introduced into the slurry chamber providing a highly efficient method of air dispersion. In the lower part of the flotation cell the rotor draws settled solids discharging them in a fan of radial jets. The stator portion of the flotation cell eliminates a rotational component of the flow from the rotor resulting in radial discharge from the rotor as desired. The result is slurry recirculation within the cell eliminating swirling of the cell contents. Swirling of the slurry is undesirable as it tends to inhibit the formation of a stable froth layer on the slurry surface. Additionally, the stator creates a zone of high shear between the rotor periphery and stator vanes aiding in the formation of fine air bubbles. The aerated flow from the rotor is naturally buoyant and as larger quantities of air are introduced into the cell the buoyancy of the rotor effluent increases as well as the opportunity for turbulent disturbances in the upper zone of the cell. In addition, at excessively low aeration levels turbulence occurs at the corners of the cell rising to the cell surface and disturbing the froth zone.
In flotation mechanisms surface turbulence of the froth zone is a primary cause of performance loss in terms of minerals detaching from their carrier air bubbles and dropping out of the froth zone into the slurry below. Surface turbulence results from nonuniform distribution of air on the surface of the flotation cell and from excessively low and high aeration volumes. At excessively low aeration levels corner turbulence occurs at the four corners of the cell while at excessively high aeration levels center turbulence occurs at the rotor shaft, with froth disturbance in each case. Additionally, if the cell is operating without good zonal separation the inflow/outflow conditions in the lower regions of the cell manifest disturbances in the upper regions of the cell including turbulence in the froth zone.
The mining/milling industry is faced with increasing pressure to cut costs while maintaining product quality and in some cases expanding production. This invention is directed to these objectives with specific reference to flotation equipment.